Hydraulic brake system

ABSTRACT

A vehicle having a hydraulic power brake system and a hydraulic power steering system, each having its own pump may utilize the power steering system pump as an emergency back up pump for the power brake system should the pump for the power brake system fail. The fluid under pressure in the accumulator for the power brake system will act upon failure of the power brake pump to initiate the switch over to the power steering pump.

United States Patent 1191 Ueda 1 Jan. 2, 1973 [54] HYDRAULIC BRAKESYSTEM [56] References Cited [75] lnventor: Atumi Ueda, Kariya, JapanUNITED STATES PATENTS [73] Assignee: Alsin Selkl Kabushikl Keisha,2,804,753 9/1957 Leduc .....60/5l UX Kariya, Japan 2,396,984 3/ 1946Broadston et a1 ..60/51 UX 3,142,962 8/1964 Lohbauer ,.6/52 S Filed: 924, 1970 3,364,821 1/1968 Gephart et a1. ..1so/79.2 R

I Appl' 7s063 Primary Examiner-Kenneth H. Betts Assistant Examiner-JohnA. Pekar 30 Foreign A n aflon p Data Attorney-Sughrue, Rothwell, Mion,Zinn 8L Macpeak Sept. 24, 1969 Japan "44775965 [57] ABSTRACT s 4 1 6 .Li 2 japan A vehicle having a hydraulic power brake system and p apan I ahydraulic power steering system, each having its own pump may utilizethe power steering system pump as [52] US. Cl. ..l 80/79.2 11,60/52 S anemergency back up pump forthe power brake ll!- Clsystem should the pumpfor the power brake system Field of seal'fll K 60/52 fail. The fluidunder pressure in the accumulator for 60/51 the power brake system willact upon failure of the power brake pump to initiate the switch over tothe power steering pump.

3 Claims, 5 Drawing Figures PATENTED N 2 i975 Q 3 708,030

sum 1 0F 3 FIG. IA

INVENTOR ATUMI UEDA ju fue 7h I BY g Mflfm K ATTORNEYS PATENV'IEDJAN2197a SHEET 3 BF 3 @Lazn HYDRAULIC BRAKE'SYSTEM This invention relatesto improvements and relating to a hydraulic power brake system adaptedfor use on a powered vehicle, especially an automotive vehicle.

The conventional hydraulic power brake system contains a hydraulic powersource, preferably a pump. Should the pump fail to operate by a certainor other cause during travel of the vehicle, the braking system wouldbecome disable to operate, resulting in a very dangerous state for thedriver and the possible passengers on board the vehicle.

The main object is to provide a hydraulic brake system of the abovekind, capable of obviating the aforementioned conventional drawback.

A further object is to provide a hydraulic brake system of the abovekind wherein under normal operating conditions of the system, a firstpump means for the brake system and a second pump means used for acertain other hydraulic system, preferably the vehicle power steeringsystem operable independently to each other, but in case of a functionalfailure of the first pump means, the second pump means is automaticallybrought into pressure fluid communication with a pressure accumulatorprovided in the hydraulic brake system for replenishing the deficientpressure energy thereto and making the latter ready for its operation.

These and further objects, advantages and features of the invention willbecome more apparent when read the following detailed description of theinvention by reference to the accompanying drawings illustrative ofseveral preferred embodiments of the invention only by way of example.

In the drawings:

FIGS. 1A and 1B constitute in combination a single drawing illustrativeof a schematic general arrangement of a first embodiment of the improvedhydraulic brake system according to this invention, wherein, however,several preferred constituents being shown each in an enlarged andlongitudinal sectional view.

FIGS. 2-4 are block diagrams illustrative of a second, a third and afourth embodiment of the invention.

Referring now to the accompanying drawings, several preferredembodiments of the invention will be described in detail hereinbelow.

At first in FIGS. 1-2, illustrative of the first embodiment of theinvention, a high pressure, low delivery type pump is provided in ahydraulic brake circuit as shown, said pump being driven from anautomotive dynamo or the like conventional primemover, although notshown.

The pump 10 is so arranged that it sucks oil from reservoir vessel 11through pipings 34 and 12, soas to elevate the oil in its pressure, thethus pressureelevated oil isconveyed through a piping 13, a check valve14 and a further piping 15 to inlet 54of a first safety valve unit 16which is formed with an outlet 62 hydraulically connected through apiping 17 to an accumulator 18. Said outlet 62 is connected at the sametime hydraulically with port 74 of a second safety valve unit 19; thefirst safety unit 16 is formed witha second outlet 61 which ishydraulically connected through pipings 20 and 200 to a furtheraccumulator 21, and through said piping 20 with further port 73 of thesecond safety valve unit l9.

The second valve unit 19 is formed with an outlet port 81 which ishydraulically connected through piping 22 to an inlet 21' of a controlvalve unit 23, the latter being further hydraulically connected throughan outlet 25' and a piping 24 to an inlet port 104 of third safety valveunit 25; an outlet port 94 of the latter is connected hydraulicallythrough piping 26 'to a wheel cylinder 27.

Another outlet port 80 of said second safety valve 19 is hydraulicallyconnected through piping 28 and inlet 21a to another control valve 29which has an outlet 25a connected through piping 30 to another inletport 103 of said third safety valve 25, an outlet port 93 of the latterbeing hydraulically connected through piping 31 to another wheelcylinder 32.

In a power steering hydraulic circuit, a low pressure, high deliverycapacity pump 33 is provided as shown, said pump 33 being arranged to bedriven from the automotive drive engine or the like primemover, also notshown.

This pump 33 sucks oil through piping 34 from reservoir vessel 11, andthe thus pressurized oil is conveyed through piping 35 to an unloadingvalve unit 36, then through an intensifier 37 to a power steering unit38 shown only schematically and then through a drain piping 39 back tosaid reservoir vessel 11 for providing a feed back oil flow.

Another inlet port of said first safety valve unit 16 is hydraulicallyconnected through piping 40, check valve 41 and a further piping 42 to aport 189 of said intensifier 37. Accumulator 18 is hydraulicallyconnected through piping 43 to an inlet port 118a of a fourth safetyvalve unit 44, while another accumulator 21 is connected through pipings200 and 45 to another inlet port 1 18 of said fourth safety valve unit44.

An outlet port 121 of valve unit 44 is connected hydraulically throughpiping 46 to a control inlet port 148 of said unloading valve unit 36.Control valve units 23 and 29 are connected through piping 47 to saidreservoir 11.

A relief valve 48 is provided between said pipings 13 and 12 and forsaid pump 10. I

First safety valve unit 16 comprises a main body 49 which is formed witha cylinder bore 50 receiving slidably therein a piston 53 which isformed with crossed passages 51 and 52. Normally, the piston 53 is sopositioned that the both ends of the passage 51 are kept in registrationwith inlet ports 54 and 55, respectively, while the ends of the passage52 form valve seats 52a and 52b, respectively cooperating'respectiveball valves 56 and 57. These ball valves are urged to move inwards byrespective valve holder pistons 58 and 59 which are received slidably ina plug 60 and the cylinder body 49, said plug being threadedly coupledwith the left-hand end of the cylinder body in FIG. 1A.

Pistons 58 and 59 are formed with respective axial bores 63 and 64. Bore63 is kept in fluid communication with outlet port 61 which is boredaxially through said plug 60, on the one hand, and with a left-handfluid chamber 65 formed within the cylinder bore 5 0 at the left-handside of piston 53, on the other hand. Bore 64 is kept in fluidcommunication with outlet port 62 which is bored axially through theright-hand end of main cylinder body 49, on the one hand, and with aright-hand fluid chamber 66 formed again within the cylinder bore 50 atthe right-hand side of piston 53, on the other. At the opposite sides ofthe piston 53 and within the fluid chambers 65 and 66, there arebalancing springs 69 and 70, respectively, for resiliently positioningthe piston 53 normally in the shown position.

Second safety valve unit 19 comprises a cylindershaped main body 71formed therein with an axial actuating chamber 72 which is capable offluidically communicating with respective inlet ports 73 and 74 whenrespective ball valves 78 and 78 are brought into their open position.More specifically, however, the port 74 is bored axially through a plug75 which is threadedly coupled with the cylinder main body 71 at itsrighthand end as shown. Ports 73 and 74 are formed with respective valveseats 76 and 77 which are normally closed as shown by said ball valves78 and 78', respectively. For this valve closing purpose, a compressionspring 79 is provided between these valve balls which are urgedresiliently to maintain their closing position shown.

The main cylinder body 71 is formed with two lateral outlet ports 80 and81 kept in communication with the actuating chamber 72 and arranged inan opposed relationship to each other and connected with respectivepipings 28 and 22, respectively.

Third safety valve unit 25 comprises a main hollow body 82 having anaxial interior bore or chamber 83 which mounts slidably a piston 84,valve holders 85 and 86 being kept in pressure contact with the oppositesides of the piston as shown. For this purpose, an urging springs 87 isprovided under compression between the lower end wall of main body 82and the holder 85. In the similar way, a further spring 88 is providedunder compression between the upper end wall of main body 82 and theholder 86. Valve members 91 and 92 are suspendedly mounted on thecentral parts of the holders 85 and 86 by means of springs 89 and 90.These valve members are so mounted that they close ports 93 and 94,respectively, when they are brought into their closing position, as willbe more fully described hereinafter. As seen, these ports 93 and 94 arehydraulically connected through pipings 31 and 26 with wheel cylinders32 and 27, respectively, as was briefly referred to hereinbefore. Valveholders 85 and 86 are formed axial grooves 850 and 86a, respectively,which communicate with chambers 95;96 and 97;98.

Main body 82 is provided with two separated stopper means 101 and 102backed upwith respective springs 99 and 100, said stopper means beingnormally kept in pressure engagement with the outside peripheries ofvalve holders 76 and 77, respectively. In case of an unbalancedcondition between the hydraulic pressures implied upon the piston 84atits both sides in the axial direction thereof, as will be more fullydescribed hereinafter, one of said stopper means will serve for fixedlypositioning one of the holders 85 and 86, so as to close one of thevalves 91 and 92. Main body 82 is formed with separated ports 103 and104 which are hydraulically connected with said pipings 30 and 24,

said hollow piston 107, said seat being adapted for cooperation with anelongated valve member which is slidably received in the axial bore 108.A chamber 111 is formed in the cylinder bore 106, a coil spring 112being positioned in said chamber 111 and one end of said spring abuttingagainst the inner end of a plug 114 which is threadedly coupled with thelower end of said body 105, for urging said piston 107 to move upwards.Thus, valve member 110 is kept in pres sure engagement with valve seat109 for keeping the latter in its closed state.

In practice, the valve member 110 abuts normally against the inside endwall surface of main body 105. A sealing ring 113 is fixedly attached tothe opposite or lower end of valve member 110 and adapted for closing anaxial bore formed through said plug 114 when the piston 107 descendsagainst the action of spring 112. Said bore 115 is kept in fluidcommunication through a lateral passage formed in the body of the plugwith an actuating chamber 117 for the piston 107. Inlet port 118 kept influid communication with the piping 45 communicates with a chamber 119which is formed at the upper end of the bore 106. Chamber 111 is kept influid communication through a lateral port 120 formed through the wallof said piston 107, with an out-.

let port 121 bored laterally through the wall of the main body 105.

Oil pressure control valve unit 23 comprises an axial stepped bore 28',a valve holder 29 being received slidably in the right-hand half of thebore 28' when seen in FIG. 1A. The right-hand end of the valve holder 29is kept normally in abutting condition with a snap ring 32' which isheld in position in the right-hand end of the inside wall surface ofcylinder bore 28'. An axial blind bore 30' is formed in the valve holderand an intermediate slide 33 is slidably received in the said blindbore. The slide 33' is formed with a ring shoulder 3a, amotion-transmitting coil spring 34 being inserted under compressionbetween said shoulder 33a and the. end wall at 30a of the said blindbore.

An axial-recess 33b is formed in the slide 33" for receiving, in apressure abutting condition, the inner end of a conventional pusher rod36 which is linked with a foot-operated brake pedal, not shown.

A second snap ring 37 is provided at the right-hand end of the blindbore 30' for limiting the extremity of the leftward stroke of theintermediate slide 33'.

A ball valve 39' is received rotatably and shiftably in a counter axialrecess 38' formed in the left-hand end of the valve holder 29. Apressure piston 41' is slidably received in the right-hand part at 40'of the stepped cylinder bore 28', a ring recess 42' being formed on theouter peripheral surface of the piston 41' and an axial bore 93' beingformed through the piston. The piston bore 93' and the chamber definedby ring recess 42' are kept in fluid communication with each otherthrough a lateral passage 44' bored through the piston.

The piston 41 normally abuts with its right-hand end against an inwardlyprojecting collar 45 formed on the cylinder bore wall 28' and definingthe critical zone between said right-hand and left-hand halves of thecylinder bore.

A valve seat 46' is formed at the left-hand extremity of the axial bore93', said valve seat being normally kept in its closed position byengagement with a valving collar 47a formed on a hollow valve member 47'which is slidably mounted in the axial bore 93'.

The valve member 47' is formed with an axial bore 50' for keepingpressure chambers 51' and 51" in fluid communication with each other, Atthe right-hand end of the bore 50', there is formed a valve seat 500'which is adapted for cooperation with ball valve 39'.

The left-hand half 40' of the cylinder bore 28' is closed at itsleft-hand end by a plug 52' which is threadedly coupled therewith, acompression springs 53' and 54' being inserted under compression betweenthe end wall 52a of said plug and the valving collar 47 and said endwall and the outer end 46' of the piston 41', respectively. In the valveunit, there are provided several sealing rings positioned at 55, and 57and 58, respectively, for establishing necessary seal among the relatedconstituent parts of the control valve unit.

A return spring 60' is inserted between the'piston 41 and the valveholder 29' under compression.

The companion control valve unit 29 has the same structure as of theforegoing unit 23 so that a further detailed analysis can be omitted forthe understanding of the invention. The unloading valve unit 36comprises a slidable spool valve member 126 formed with three separatedlands 123, 124 and 125 and received in a sleeve 122. The left-hand endof the spool valve 126 is exposed to the hydraulic liquid contained in achamber 127 and a piston-like spring mount 128 abutting against saidvalve end under pressure exerted by a spring 129 which abuts with itsone end on the end wall part shown at 127a and with opposite end on saidmount 128.

The chamber 127 is hydraulically connected through a port 130 and apiping 131 to the reservoir 11.

Normally, the spool valve 126 is so positioned that its central land 124is kept in substantial registration with the center of a ring recess 132formed in the wall of 5 sleeve 122. When the valve member 126 isactuated in the manner to be described, the land 124 is brought intoengagement with a ring shoulder 133, so as to establish an interruptionof fluid flow thereat.

The left-hand land 123 interrupts normally fluid communication betweentwo separated ring chambers 134 and v 135. When, however, the spoolvalve is brought into actuation in the manner to be described, a fluidcommunication will be established between these chambers.

A further chamber 136 formed in the valve unit is kept in fluidcommunication through a duct 137 with chamber 127 which is kept incommunication with the reservoir 11, as was referred to hereinbefore.

Ball valve chamber 139 is positioned in proximity to said chamber 136,through the intermediary of an inwardly projecting ring wall 201. Aplunger part 140 constitutes a part of the spool valve which extendsoutwardly of the right-hand land 125 and is kept in pressure contactwith the ball valve 138. A valve seat 141 is formed on the ring wall201, being provided for cooperation with the ball valve. Theball valveis, however, normally kept in engagement with a further valve seat 142formed on a ring wall 202, the latter seat having a smaller valveopening than that of the former seat 141. It should be noted that thepressure-receiving area of the plunger part 140 is so selected as tohave an intermediate value between the larger valve opening at 141 andthe smaller valve opening at 142.

In close proximity of the second ring wall 202, a chamber 143 is formedand a smaller plunger 144 extends from within the chamber 143 and keptin engagement with the ball valve 138. The smaller plunger 144 is formedwith an axial groove 145 for bringing the chambers 139 and 143 intofluid communication with each other, even when the valve 138 is kept inits operating condition.

At the right-hand end of the plunger 144, a spring mount 146 is kept inpressure contact, a compression spring 147" being inserted between thelatter and the end wall part 143a of the valve unit which is furtherformed with an inlet port 148 connected with the piping 146. The unit isfurther formed with a lateral port 149 which is connected with thepiping 35.

intensifier 37 comprises larger diameter chambers 150 and 151 and asmaller diameter chamber 152, a stepped piston having a larger piston153 and a smaller piston 154 being slidably received in these chambersin combination.

To the left-hand side of the chamber 150, there is provided a sleevewhich receives slidably a valve plunger 161 having valve lands 156, 157,158 and 159 and a valve part 156'. This valve plunger is normally sopositioned that its land 159 keeps the chambers 162 and 150 in fluidcommunication with each other, while the land 158 interrupts fluidcommunication between the chambers 162 and 163 and the land 157interrupts communication between the chambers 164 and 165, respectively.Under these normal operating-conditions, the land 156 keeps the chamber166 and a duct 167 in fluid communication with each other. At thisstage, chamber 166a is kept through ducts 167 and 174 in fluidcommunication with the chamber 163.

When the valve plunger 163 is actuated in the manner to be described,valve part 156' is kept in pressure engagement with valve seat 168 andcommunication between the chambers 166 and 167 is interrupted. Land 157keeps the chambers 164 and in fluid communication and at the same time,the chambers 163 and 162 are kept also in fluid communication. Land 159is kept in its advanced position into engagement with sleeve land 169,thereby fluid communication between chambers 162 and 150 beinginterrupted. At this stage, the chambers 162 and 132 are kept in fluidcommunication with each other through a duct 170 which extends through aduct 171 to check valve 172, thence through duct 173 to the chamber 152.Duct 167 communicates through ducts 174 and 175 to the chambers 163 and151, respectively. The chamber 150 communicates through a duct 176 withthe chamber 164.

Above the valve plunger 161, a small auxiliary piston 177 adapted forcarrying out a change-off operation to be described is provided whichprotrudes into the chamber 150 and brought into cooperative contact withthe piston 155 in the course of the operation of the intensifier, aswill be more fully described hereinafter.

The pusher piston 177 is urged to move towards right under the action ofspring 179 which is mounted in the chamber 178. The left-hand actuatingchamber 180 for the pusher piston 177 is kept in fluid communicationthrough duct 181 with the chamber 166, and with ducts 182, 184 and 185.The chamber 134 communicates with the duct 185. The duct 185communicates through a piping 186 with the power steering unit 38.

Chamber 151 is kept in communication through a duct 183 with a duct 184.Chamber 165 communicates through a duct 187 and chamber 178 does througha duct 188 to the duct 184, respectively. Chamber 152 communicatesthrough a duct 189 with the piping 42.

The operation of the first embodiment so far shown and described is asfollows:

Under normal braking conditions, the pump 10 sucks oil through pipings34 and 12 from the reservoir 11, as was referred to hereinbefore, thethus pressurized oil being conveyed from the pump through the piping 13,the now forcibly opened check valve 14 and the piping 15 to inlet port54 of the first safety valve unit 16, thence to the passages 51 and 52.By the provision of check valve 41, oil can not flow from the passage 51through the piping 40 to 42.

Therefore, the pressure oil delivered from the pump will act upon theball valves 56 and 57 against the action of urging springs 69 and 70,respectively, thus flowing into the chambers 65 and 66.

The oil is conveyed through respective passages 63 and 64 in the piston58 and 59 into the ports 61 and 62, thence through pipings and 17 to theaccumulators 21 and 18, respectively, for being accumulated therein.

The thus accumulated oil will flow through the inlet ports 73 and 74 ofthe second safety valve unit 19 to the chamber 81 upon forcibly openingvalves 78 and 78 against the action of spring 79. Oil is then conveyedfrom output ports 80 and 81 through pipings 28 and 22 to control valves21a and 21a respectively.

The pressure oil in the accumulator 21 and 18 is kept in communicationwith the inlet ports 118 and 118a of the fourth safety valve unit 44,thereby keeping the piston 107 at its predetermined balanced position.

The pressure oil contained in'the accumulator 18 is kept incommunication through passage 43, inlet port 118a and passage 115 to thechamber 111. The pressure prevailing in the chamber 111 is kept incommunication through passage 120, port 121 and piping 46 to the port148 of the unloading valve unit 36, thence through chamber 143, passage145 and the now opened valve seat 142 to the chamber 139. By thisconveyed oil pressure, plunger 140 is urged to move leftwards, therebythe spool valve 126 being moved also leftwards.

At this stage, ball valve 138 is urged to engage with the valve seat 141under the influence of spring 147, the spool valve 126 being urged tomove leftwards, with its land 124 interrupting fluidcommunication-between the chambers 135 and 132 and with its land 123maintaining the communication between the chambers 134 and 135.

Therefore, the sucked oil by the operating pump 33 is delivered throughpiping 35, passage 149, chambers 135 and 134, passage 185 and piping 186to the power steering unit 38, thence through piping 39 back to thereservoir 11. Under these operating conditions, the intensifier 37 is inits inoperative position so to speak.

Under these conditions, when the vehicle driver should depress the brakepedal, so as to advance the pusher rod 36, the transmission member 33being urged to move leftwards and the holder 29' being also shiftedleftwards through the intermediary of the spring 34. Thus, ball valve39' is brought into engagement with its valve seat 50a, thereby fluidcommunication between pressure chamber 51 and reservoir 11 beinginterrupted.

With further actuation of the brake pedal, the valve 47' will be shiftedleftwards under the action of a spring 53 and the valving projection 47ais separated from its seat 46'. Therefore, the accumulated pressure oilwill flow through passage 44 into the chamber 51'- and then out throughthe port 25. Since the oil pressure prevailing in the chamber 51 willact upon the crosssectional area of the valve rod part 48' of the valvemember 47', the operator senses a corresponding brake pedal reaction inan effective manner.

With the brake pedal still further depressed, the lefthand end of themember 33' will brought into direct contact with the end wall in themember 32, with or without further compression of spring 34, and thelefthand end of the member 29 will be brought into engagement with thepiston 41'. At this stage, the brake reaction is sensed in terms of thehydraulic pressure prevailing in the chamber 51' and acting upon thecross-sectional area of the piston 41', thus the brake reaction beingabruptly increased. Therefore, the piston will act as a kind of stoppermeans.

Now, when it is assumed that the accumulator should fail to operate, itwill be easily acknowledged that the left-hand end of the member 29 willurge the piston 41' to move leftwards, as in the similar way as abovedescribed in case of a brake application, the piston moving against theaction of spring 54' and the pressure prevailing in the chamber 51'being caused to elevate.

Oil pressure delivered from respective outlet ports 25a and 25' ofcontrol valves 23 and 29 is conveyed through pipings 30 and 24,respectively, to the inlet ports 103 and 104 of the third safety valveunit 25,

thence through the chambers 96 and 98 and passages a and 86b to thechambers and 97, respectively, thence further through outlet ports 93and 94 and pipings 31 and 26 to the respective wheel cylinders 32 and27, for performing the braking action.

Next, consider the abnormal operating condition where either one of theaccumulators 21 and 18, as an example the latter should fail to operate,no oil pressure will be available in the right-hand chamber 66 in thefirst safety valve unit 16, the balance piston 53 being subjected to thecorresponding hydraulic urging pressureto move it leftwards. Therefore,the piston will be moved rightwards against the action of spring 68 andvirtue of the very existence of the hydraulic urging pressure prevailingin the left hand chamber 65. The valve 57 is naturally kept in itsengaging position with its seat 52b for closing the latter. The valveholder 59 is brought into its stopped position in engagement with thecorresponding wall, thereby the port 62 being brought into its fluidflow-interrupting position. Oil will be delivered through port 61.

At the same time, it will be seen that no oil pressure is applied to theport 74 of the second safety valve unit 19, the valve 78' is kept in itsengaging position with its mating valve seat 77, under the combinedurging force exerted by spring 79 and the hydraulic pressure prevailingin the chamber 72. Therefore, pressure oil will flow in exclusivelythrough the port 73.

In the fourth safety valve unit 44, it will be seen that no pressure oilprevails in piping 43, port 118a and chamber 117, the valve and thepiston 107 kept in engagement with each other, and the thus establishedassembly will descend under the hydraulic pressure prevailing in thechamber 119 and against the action of spring 112, until the lowerend ofvalve 110 is brought into engagement with the inner end 1140 of the plug114 so as to interrupt the port 115 as the sealing pressure, thehydraulic pressure acting upon the sealing member 113 is utilized.

At the next stage, the piston 107 only is brought into engagement withthe plug end wall 114a, the valve member 110 being caused to separatefrom its mating valve seat 109. The hydraulic pressure prevailing in thechamber 119 is conveyed to the unloading valve 36 through passage 108,chamber 111, passage 120, outlet port 121 and piping 46, as in theforegoing way, so as to bring the intensifier 37 into its non-operatingposition.

Under these operating conditions, the pressure oil delivered from pump10 will flow into the chamber 65 of the first safety valve unit 16,thence through port 61 to the accumulator 21 for being stored therein.Part of the thus accumulated pressure oil will be conveyed to the port118 of the fourth safety valve unit 44 and part of the oil will flowthrough the port 73 of the second safety valve unit 19 so as to open thevalve 78 against the action of spring 79, thence the chamber 72 andports 80 and 81 for communication to the control valves 23 and 29. Theremaining braking operation is similar to that described hereinbefore,and thus no further analysis thereof would be necessary to set forth forbetter understanding of the invention.

Should either one of the hydraulic circuits leading from the thirdsafety valve unit 25 to the wheel cylinders 27 and 32 from a certain orother cause, for instance, the piping 26, fail to operate, the pressureprevailing in the chamber 98 will not be caused to elevate at thebeginning stage of the brake application.

Therefore, at this stage, the piston 84 will be elevated in its positionunder the hydraulic pressure in the chamber 95 and against the springaction at 88. Thus, the valve 111 is kept in its seated position, so asto keep its related port in its flow-interrupting position. Stop member102 will be kept in engagement with groove or recess 86a under thespring action at 100. Therefore, in the further stage, the chamber 98 iskept in a sealed condition and fluid communication between control valve23 and wheel cylinder valve 138 will be caused to separate from contactwith its cooperating larger valve seat 141 and to shift rightwards so asto engage the smaller valve seat 142, thus the spool valve 126 beingkept in the shown position. Pressure oil delivered from pump 33 will beconveyed through piping 35 and the port 149 of unloading valve unit 36into the chambers 135 and 132, thence'through passage 170 into theacting chamber 162 of the valve plunger, and further into the chamber150. At this stage, 37 is kept in an interrupted state.

Should the pump 10 fail to operate and no pressure accumulating job isbeing performed, or there is only insufficient delivery capacity of thepump 10 be available so as not to replenish the consumed pressure oil ina sufficient way, or in a starting stage of the drive engine so that theoil pressure delivered from the pump is insufficient to meet with theoperational demands, the chamber 151 is kept in fluid communicationthrough passages 175 and 167, chamber 166, passages 181, 182 and 184 tothe reservoir 11. The passage 176 and the chamber 164 are kept in sealedcondition as shown in FIG. 1. Therefore, the pressure in the chamber iscaused to elevate and the piston is shifted towards right. Thus, theright-hand chamber 152 is increased in its prevailing pressure, the thusincreased oil pressure being conveyed through passage 189 and piping 42to the acting chambers 65 and 66 of the first safety valve unit 16,thence through ports 61 and 62 into the accu* mulators 21 and 18. Thethus accumulated pressure oil will be utilized in the aforementionedway.

When the hydraulic pressure in the chamber 150 attains a predeterminedvalue, plunger 161 receiving the hydraulic pressure at its right-handend surface 159 is shifted leftwards in FIG. 18 against the action ofspring 166', and liquid communication between chamber 166 and passage167 is interrupted by the left-hand valve land 156, with the right-handland 158 opening and establishing a liquid communication between thechambers 163 and 162, thereby valve land 156 being acted upon by thepump pressure and the valve plunger 161 being further shifted leftwardsagainst the action of spring 166'. In this way, valve land 159 isbrought into such position as to interrupt liquid communication betweenchambers 150 and 152. At the same time, valve land 157 will shiftleftwards, so as to establish a liquid communication between thechambers 164 and 165, thereby oil pressure in the chamber 150 beingconveyed through duct 176, chambers 164 and 165, and ducts 187 and 184to the low pressure circuit 186. Thus, the oil pressure from pump 33will be conveyed through ducts 174 and 175 to the chamber 151, therebyurging the piston 155 reversebly toward left. In this case, the pressureoil supply to the chamber 152 is performed through check valve 172.

When the left-hand end of the piston 155 is brought into engagement withauxiliary piston 177, the latter being urged to move leftwards from theposition shown in FIG. 1B and against the action of spring 179. Thus, atfirst, port or duct 182 is interrupted and the hydraulic pressureprevailing in the chamber and duct 181 are elevated, bringing thehitherto closing valve land 156 in its valve-open position andestablishing a liquid communication between duct 167 and chamber 166. Bythis operation, valve plunger 161 is returned to the position shown inFIG. 18. Further, the pressure oil conveyed form pump 33 will act uponthe piston 155 which is shifted thereby towards left, so as to provide apumping action as before, and so on.

By repeating the above-mentioned operation, a prescribed oil pressurewill be accumulated in the accumulators 18 and 21.

Upon accumulation of the necessary oil pressure in these accumulators inthis way, oil pressure conveyed through the fourth safety valve unit 44to the plunger 126 of the unloading valve 36 act to the plunger 126 ofthe unloading valve 36 act to the plunger for shifting it leftwards andthe pump pressure will be returned through the low pressure circuit 186to reservoir 11.

As for the arrangement shown in FIGS. 1A and 1B in combination, thereare provided two independent pumps 10 and 33, accumulator means andother pumping means in the hydraulic brake circuit. Such arrangement canbe modified in its connection mode as shown in FIG. 2. In this modifiedarrangement, two independent pumps 10 and 33 are included in respectivehydraulic circuits. More specifically, the low pressure, high deliverycapacity pump 33 is used in the powersteering circuit, while the highpressure, low delivery capacity pump is used in the hydraulic brakecircuit, the former pump being arranged to be used as an auxiliary meansfor the latter circuit.

When the pump 10, for instance, should fail to operate, the pilotpressure in the accumulator means 18(21) will be utilized for actuationof unloading valve unit 36, so as to deliver pressure oil from pump 33through piping 209, check valve 210 and further piping 211 toaccumulator means 18(21) for being accumulated therein.

A still further modified arrangement shown in FIG. 3 is so connected asto include two hydraulic brake systems instead of a sole hydraulic brakesystem as is the case shown in FIG. 2.

When the accumulator 18 should fail to operate as an example, the firstsafety valve 16 is actuated as in the case shown in FIGS. 1A and 1B incombination, so as to interrupt the piping 62, while the fourth safetyvalve unit 44 is actuated for leading the pilot pressure from theremaining accumulator 21 to the unloading valve unit 36. In this way,the pressure oil delivered from pump 10 will open forcibly the checkvalve 14 so to supply pressure oil to the first safety valve unit 16.The remaining accumulator 21 will receive pressure oil as usual forpressure accumulation.

In a still further modified arrangement shown in FIG. 4 the intencifier37 is added to the arrangement shown in FIG. 2.

Should the pump 10 fail to operate, the pressure oil is delivered frompump 33 to accumulator 18(21) at a same pressure as that of the pump 10.By the actuation of the unloading valve 36, the intensifier 37 is alsoactuated in the similar way as was described hereinbefore byconsultation with FIG. 1. The thus pressure-increased oil is furtherconveyed through piping 209, check valve 210 and further piping 211 tothe accumulator 18(21) for being charged therein. Thus, also in thiscase, the braking effect can be brought about with use of regularhydraulic'pressure.

It will be clear from the foregoing that the low pressure, high deliverypump arranged for the power steering and the high pressure, low deliverypump for the braking purpose are actuated simultaneously for theattributed respective services. However, if a failure should occur inthe pressure source of the hydraulic brake system, the power-steeringpumpor the pump pressure in an intensified state will be utilized forthe said first servo motor, accumulator means fluidically connected insaid closed hydraulic circuit means, control valve means fluidicallyconnected with said first servo motor and said accumulator means forestablishing fluid communication therebetween inresponse to manualoperation of said control valve means, first ump eafis in said closedcircuit means for pumping ydrau 1C uid under pressure to said accumuator means, and open hydraulic circuit means for fluidically connectingsaid second servo motor with said hydraulic pressure source means,second pump means in said open hydraulic circuit means for pumpinghydraulic fluid under pressure to said second servo motor, unloadingvalve means in said open hydraulic circuit means, means connecting saidclosed hydraulic circuit means to said unloading valve means wherebysaid unloading valve means may act under the influence of the hydraulicpressure prevailing in said closed hydraulic circuit means, andadditional means connecting said unloading valve means to saidaccumulator valve means so that said unloading valve means is adapted todeliver hydraulic fluid under pressure from said second pump means tosaid accumulator means when the pressure of the hydraulic fluid fromsaid first pump means falls below a predetermined pressure.

2. A hydraulic control system as set forth in claim 1 further.comprising an intensifier means connected between said unloading valvemeans and said accumulator means for intensifying the pressure of thehydraulic fluid conveyed from said second pump means to said accumulatormeans.

3. A hydraulic control system as set forth in claim 1 wherein said firstservo motor is comprised of a pair of hydraulically energizable brakemeans, said control valve means being operable to control the connectionof said accumulators with said brake means in response to actuation of abrake pedal and first safety valve means is provided in said closedhydraulic circuit for interruption of hydraulic pressure in the relatedhydraulic system including either of said accumulators should it becomedisabled.

I! l I

1. A hydraulic control system for a powered vehicle comprising hydraulicsource means, first and second hydraulic servo motors, closed hydrauliccircuit means containing said hydraulic pressure source means and saidfirst servo motor, accumulator means fluidically connected in saidclosed hydraulic circuit means, control valve means fluidicallyconnected with said first servo motor and said accumulator means forestablishing fluid communication therebetween in response to manualoperation of said control valve means, first pump means in said closedcircuit means for pumping hydraulic fluid under pressure to saidaccumulator means, and open hydraulic circuit means for fluidicallyconnecting said second servo motor with said hydraulic pressure sourcemeans, second pump means in said open hydraulic circuit means forpumping hydraulic fluid under pressure to said second servo motor,unloading valve means in said open hydraulic circuit means, meansconnecting said closed hydraulic circuit means to said unloading valvemeans whereby said unloading valve means may act under the influence ofthe hydraulic pressure prevailing in said closed hydraulic circuitmeans, and additional means connecting said unloading valve means tosaid accumulator valve means so that said unloading valve means isadapted to deliver hydraulic fluid under pressure from said second pumpmeans to said accumulator means when the pressure of the hydraulic fluidfrom said first pump means falls below a predetermined pressure.
 2. Ahydraulic control system as set forth in claim 1 further comprising anintensifier means connected between said unloading valve means and saidaccumulator means for intensifying the pressure of the hydraulic fluidconveyed from said second pump means to said accumulator means.
 3. Ahydraulic control system as set forth in claim 1 wherein said firstservo motor is comprised of a pair of hydraulically energizable brakemeans, said control valve means being operable to control the connectionof said accumulators with said brake means in response to actuaTion of abrake pedal and first safety valve means is provided in said closedhydraulic circuit for interruption of hydraulic pressure in the relatedhydraulic system including either of said accumulators should it becomedisabled.